Polishing pad with window for planarization

ABSTRACT

The present invention relates to a polishing pad. In particular, the polishing pad of the present invention can include a window. The polishing pad of the present invention can be useful for polishing articles and can be especially useful for chemical mechanical polishing or planarization of a microelectronic device, such as a semiconductor wafer. The window of the polishing pad is at least partially transparent and thus, can be particularly useful with polishing or planarizing tools that are equipped with through-the-platen wafer metrology.

[0001] The present invention relates to a polishing pad. In particular,the polishing pad of the present invention can include a window. Thepolishing pad of the present invention can be useful for polishingarticles and can be especially useful for chemical mechanical polishingor planarization of a microelectronic device, such as a semiconductorwafer. The window of the polishing pad is at least partially transparentand thus, can be particularly useful with polishing or planarizing toolsthat are equipped with through-the-platen wafer metrology.

[0002] In general, the polishing or planarization of a non-planarsurface of a microelectronic device to an essentially planar surfaceinvolves rubbing the non-planar surface with the work surface of apolishing pad using a controlled and repetitive motion. A polishingslurry can be interposed between the rough surface of the article thatis to be polished and the work surface of the polishing pad.

[0003] The fabrication of a microelectronic device such as asemiconductor wafer generally involves the formation of a plurality ofintegrated circuits on the wafer comprising, for example, silicon orgallium arsenide. The integrated circuits can be formed by a series ofprocess steps in which patterned layers of materials, such asconductive, insulating and semiconducting materials, are formed on thesubstrate. In order to maximize the density of integrated circuits perwafer, it is desirable to have an essentially planar polished substrateat various stages throughout the semiconductor wafer production process.Thus, semiconductor wafer production can include at least one, and moretypically a plurality of polishing steps, which can use one or morepolishing pads.

[0004] A chemical mechanical polishing (CMP) process can include placingthe microelectronic substrate in contact with a polishing pad; rotatingthe pad while a force is applied to the backside of the microelectronicdevice; and applying an abrasive-containing chemically-reactive solutioncommonly referred to as a “slurry” to the pad during polishing. A CMPpolishing slurry can contain an abrasive material, such as silica,alumina, ceria or mixtures thereof. The rotational movement of the padrelative to the substrate as slurry is provided to the device/padinterface can facilitate the polishing process. In general, polishingcan be continued in this manner until the desired film thickness isremoved.

[0005] Depending on the choice of polishing pad and abrasive, and otheradditives, the CMP process can provide effective polishing at desiredpolishing rates while reducing or minimizing surface imperfections,defects, corrosion, and erosion.

[0006] Polishing or planarization characteristics can vary frompad-to-pad, and throughout the operating lifetime of a given pad.Variations in the polishing characteristics of the pads can result ininadequately polished or planarized substrates which are not useful.Thus, it is desirable in the art to develop a polishing pad thatexhibits reduced pad-to-pad variation in polishing or planarizationcharacteristics. It is further desirable to develop a polishing pad thatexhibits reduced variations in polishing or planarizationcharacteristics throughout the operating life of the pad.

[0007] Planarizing tools having the ability to measure the progress ofthe planarization process while the wafer is held in the tool and incontact with the pad are known in the art. Measuring the progress ofplanarizing a microelectronic device during the planarizing process canbe referred to in the art as “in-situ metrology”. U.S. Pat. Nos.5,964,643 and 6,159,073; and European Patent 1,108,501 describepolishing or planarizing tools and in-situ metrology systems. Ingeneral, in-situ metrology can include directing a beam of light throughan at least partially transparent window located in the platen of thetool; the beam of light can be reflected off the surface of the wafer,back through the platen window, and into a detector. The polishing padcan include a window that is at least partially transparent to thewavelengths used in the metrology system, and essentially aligned withthe planten window.

[0008] Thus, it is desirable to develop a polishing pad that comprises awindow area useful for in-situ metrology. It is further desirable thatthe window provides suitable transparency throughout the operating lifeof the pad.

[0009] One disadvantage with known pads having windows which arecoplanar with the polishing surface, can include wearing of the windowportion at a slower rate than the pad surface. A further disadvantagewith known pads having a coplanar window can include scratching of thewindow as a result of its contact with abrasive particles in the slurryduring the polishing or planarization process. A scratched window cangenerally reduce the transparency of the window and can cause anattenuation of the metrology signal.

[0010] The present invention includes a polishing pad having a window.In a non-limiting embodiment, the polishing pad can comprise a firstlayer and a second layer. The first layer can function as the worksurface or polishing layer of the pad. At least a portion of the secondlayer can comprise a window which is at least partially transparent towavelengths used by the metrology instrumentation of polishing tools.Furthermore, the first layer can absorb at least 2 percent by weight ofpolishing slurry based on the total weight of the first layer.

[0011] The polishing pad of the present invention can comprise a firstlayer and a second layer. The first layer can function as the polishingor working surface of the pad such that the first layer can at leastpartially interact with the substrate to be polished and the polishingslurry. In a non-limiting embodiment, the first layer can be porous andpermeable to polishing slurry. In a non-limiting embodiment, the secondlayer can be substantially nonporous and substantially impermeable topolishing slurry.

[0012] As used herein and the claims the term “substantially nonporous”means generally impervious to the passage of liquid, gas, and bacteria.On a macroscopic scale, a substantially nonporous material exhibits fewif any pores. As used herein and the claims, the term “porous” meanshaving pore(s) and the term “pore(s)” refers to minute opening(s)through which matter passes.

[0013] It is noted that, as used in this specification, the singularforms “a,” “an,” and “the” include plural referents unless expressly andunequivocally limited to one referent.

[0014] For the purposes of this specification, unless otherwiseindicated, all numbers expressing quantities of ingredients, reactionconditions, and so forth used in the specification and claims are to beunderstood as being modified in all instances by the term “about.”Accordingly, unless indicated to the contrary, the numerical parametersset forth in the following specification and attached claims areapproximations that may vary depending upon the desired propertiessought to be obtained by the present invention. At the very least, andnot as an attempt to limit the application of the doctrine ofequivalents to the scope of the claims, each numerical parameter shouldat least be construed in light of the number of reported significantdigits and by applying ordinary rounding techniques.

[0015] Notwithstanding that the numerical ranges and parameters settingforth the broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contain certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements.

[0016] The first layer can include a variety of materials known in theart. Non-limiting examples of suitable materials comprising the firstlayer can include but are not limited to particulate polymer andcrosslinked polymer binder as described in U.S. Pat. No. 6,477,926B1;particulate polymer and an organic polymer binder as described in U.S.patent application Ser. No. 10/317,982; sintered particles ofthermoplastic resin as described in U.S. Pat. Nos. 6,062,968; 6,117,000;and 6,126,532; and pressure sintered powder compacts of thermoplasticpolymer as described in U.S. Pat. Nos. 6,231,434B1; 6,325,703B2;6,106,754; and 6,017,265. Further non-limiting examples of suitablematerials comprising the first layer can include polymeric matricesimpregnated with a plurality of polymeric microelements, wherein eachpolymeric microelement can have a void space therein, as described inU.S. Pat. Nos. 5,900,164 and 5,578,362.

[0017] The thickness of the first layer can vary. In alternatenon-limiting embodiments, the first layer can have a thickness of atleast 0.020 inches, or at least 0.040 inches; or 0.150 inches or less,or 0.080 inches or less.

[0018] In another non-limiting embodiment, the first layer can includepores such that polishing slurry can be at least partially absorbed bythe first layer. The number of pores can vary. In alternate non-limitingembodiments, the first layer can have a porosity, expressed as percentpore volume, of at least 2 percent by volume based on the total volumeof the first layer, or 50 percent or less by volume based on the totalvolume of the first layer, or from 2 to 50 percent by volume based onthe total volume of the first layer.

[0019] The percent pore volume of the polishing pad layer can bedetermined using a variety of techniques known in the art. In anon-limiting embodiment, the following expression can be used tocalculate percent pore volume:

100×(density of the pad layer)×(pore volume of the pad layer).

[0020] The density can be expressed in units of grams per cubiccentimeter, and can be determined by a variety of conventional methodsknown in the art. In a non-limiting embodiment, the density can bedetermined in accordance with ASTM D 1622-88. The pore volume can beexpressed in units of cubic centimeters per gram, and can be determinedusing conventional methods and equipment known in the art. In anon-limiting embodiment, pore volume can be measured in accordance withthe mercury porosimetry method in ASTM D 4284-88, using an Autopore IIImercury porosimeter from Micromeritics can be used. In a furthernon-limiting embodiment, the pore volume measurements can be made underthe following conditions: a contact angle of 140°; a mercury surfacetension of 480 dynes/cm; and degassing of the polishing pad layer sampleunder a vacuum of 50 micrometers of mercury.

[0021] In a non-limiting embodiment, the first layer can have an atleast partially open structure such that it can absorb slurry. Inalternate non-limiting embodiments, the first layer can absorb at least2 percent by weight of polishing slurry based on the total weight of thefirst layer, or not more than 50 percent by weight, or from 2 percent byweight to 50 percent by weight.

[0022] In another non-limiting embodiment of the present invention, thefirst layer of the polishing pad can have a compressibility greater thanthe second layer. As used herein, the term “compressibility” refers tothe percent volume compressibility measurement. In a furthernon-limiting embodiment, the percent volume compressibility of the firstlayer can be at least 0.3 percent; or 3 percent or less; or from 0.3 to3 percent; when a load of 20 psi is applied.

[0023] The percent volume compressibility of a pad layer can bedetermined using various methods known in the art. In a non-limitingembodiment, the percent volume compressibility of a pad layer can bedetermined using the following expression.$100 \times \frac{( {{{pad}\quad {layer}\quad {volume}\quad {without}\quad {load}} - {{pad}\quad {layer}\quad {volume}\quad {under}\quad {load}}} )}{( {{pad}\quad {layer}\quad {volume}\quad {without}\quad {load}} )}$

[0024] In a non-limiting embodiment, the area of the pad layer does notchange when the load is placed on it; thus, the preceding equation forvolume compressibility can be expressed in terms of pad layer thicknessby the following expression.$100 \times \frac{( {{{pad}\quad {layer}\quad {thickness}\quad {without}\quad {load}} - {{pad}\quad {layer}\quad {thickness}\quad {under}\quad {load}}} )}{( {{pad}\quad {layer}\quad {thickness}\quad {without}\quad {load}} )}$

[0025] The pad layer thickness can be determined using a variety ofknown methods. In a non-limiting embodiment, the pad layer thickness canbe determined by placing a load (such as, but not limited to, calibratedweights) on the pad sample and measuring the change in thickness of thepad layer as a result of the load. In a further non-limiting embodiment,a Mitutoyo Electronic Indicator, Model ID-C112EB can be used. Theindicator has a spindle or threaded rod which can be fitted at one endwith a flat contact under which the pad layer is placed. The spindle canbe fitted at the other end with a device for applying specified loads tothe contact area, such as but not limited to a balance pan which acceptscalibrated weights. The Indicator displays the displacement of the padlayer resulting from applying the load. The Indicater display istypically representative of inches or millimeters. The ElectronicIndicator can be mounted on a stand, such as a Mitutoyo PrecisionGranite Stand, to provide stability while taking the measurements. Thelateral dimensions of the pad layer can be sufficient to permitmeasurements at least 0.5″ from any edge. The surface of the pad layercan be flat and parallel over a sufficient area to permit uniformcontact between the test pad layer and the flat contact. The pad layerto be tested can be placed under the flat contact. The thickness of thepad layer can be measured prior to applying the load. Calibrated balanceweights can be added to the balance pan for a specific resultant load.The pad layer then can be compressed under the specified load. TheIndicator can display the thickness/height of the pad layer under thespecified load. The thickness of the pad layer prior to applying theload minus the thickness of the pad layer under the specified load canbe used to determine the displacement of the pad layer. In anon-limiting embodiment, a load of 20 psi can be applied to the padlayer. Measurements can be made at a standardized temperature such asroom temperature. In a non-limiting embodiment, measurements can betaken at a temperature of 22° C+/−2° C.

[0026] In alternate non-limiting embodiments, the above-described methodof measuring pad layer thickness can be applicable to a stacked padassembly or layer(s) comprising the stacked pad assembly.

[0027] In a non-limiting embodiment, a procedure for measuring percentvolume compressibility can include placing the contact on the granitebase and adjusting the indicator to read zero. The contact can then beraised and the specimen placed on the granite stand under the contactwith the edge of the contact at least 0.5″ from any edge of thespecimen. The contact can be lowered onto the specimen and the specimenthickness measurement can be taken after 5+/−1 seconds. Without movingthe specimen or the contact, sufficient weight can be added to the panto cause a force of 20 psi to be applied to the specimen by the contact.The reading for the specimen thickness under load measurement can bemade after 15+/−1 seconds. The measurement procedure can be repeated,making five measurements at different positions on the specimen at least0.25″ apart using 20 psi of compressive force.

[0028] In a non-limiting embodiment, the softness of the first layer canbe determined. As used herein and the claims, the term “softness” refersto the Shore A Hardness of the material. In general, the softer thematerial, the lower the Shore A Hardness value. In alternatenon-limiting embodiments, the first layer can have a Shore A Hardness ofat least 85; or 99 or less, or from 85 to 99. The Shore A Hardness valuecan be determined using various methods and equipment known in the art.In a non-limiting embodiment, Shore A Hardness can be determined inaccordance with the procedure recited in ASTM D 2240, using a Shore“Type A” Durometer having a maximum indicator (available from PCTInstruments, Los Angeles, Calif.). In a non-limiting embodiment, thetest method for Shore A Hardness can include the penetration of aspecific type of indentor being substantially forced into the testmaterial under specified conditions. In this embodiment, the Shore AHardness can be inversely related to the penetration depth and can bedependent on the elastic modulus and viscoelastic behavior of the testmaterial.

[0029] In a non-limiting embodiment, the first layer can comprisegrooves or pattern on the work or polishing surface. The types ofgrooves and/or patterns can vary and can include the various types ofgrooves and/or patterns known in the art. The process for making thegrooves and patterns can also vary and can include the variousconventional methods known in the art.

[0030] The polishing pad of the present invention further comprises asecond layer. In a non-limiting embodiment, the second layer can beconnected to at least a portion of the first layer. In a furthernon-limiting embodiment, the first layer can be connected to at least aportion of the second layer, and the second layer can be connected to atleast a portion of an optional third layer.

[0031] The second layer can include a variety of materials known in theart. The second layer can be selected from substantially non-volumecompressible polymers and metallic films and foils. As used herein andthe claims, “substantially non-volume compressible” means that thevolume can be reduced by less than 1% when a load of 20 psi is applied.In a non-limiting embodiment, the method for applying the load andmeasuring the reduction in volume is previously described herein can beemployed.

[0032] Non-limiting examples of substantially non-volume compressiblepolymers can include polyolefins, such as but not limited to low densitypolyethylene, high density polyethylene ultra-high molecular weightpolyethylene and polypropylene;

[0033] polyvinylchloride; cellulose-based polymers, such as but notlimited to cellulose acetate and cellulose butyrate; acrylics;polyesters and co-polyesters, such as but not limited to PET and PETG;polycarbonate; polyamides, such as but not limited to nylon 6/6 andnylon 6/12; and high performance plastics, such as but not limited topolyetheretherketone, polyphenylene oxide, polysulfone, polyimide, andpolyetherimide; and mixtures thereof.

[0034] Non-limiting examples of metallic films can include but are notlimited to aluminum, copper, brass, nickel, stainless steel, andcombinations thereof.

[0035] The thickness of the second layer can vary. In alternatenon-limiting embodiments, the second layer can have a thickness of atleast 0.0005, or at least 0.0010; or 0.0650 inches or less, or 0.0030inches or less.

[0036] In a non-limiting embodiment, the second layer can be flexible toenhance or increase the uniformity of contact between the polishing padand the surface of the substrate being polished. A consideration inselecting the material for the second layer can be the capability of amaterial to provide compliant support to the work surface of thepolishing pad such that the first layer substantially conforms to themacroscopic contour or long-term surface of the device being polished. Amaterial having said capability can be desirable for use as the secondlayer in the present invention.

[0037] The flexibility of the second layer can vary. The flexibility canbe determined using a variety of conventional techniques known in theart. As used herein and the claims the term “flexibility” (F) refers tothe inverse relationship of second layer thickness cubed (t³) and theflexural modulus of the second layer material (E), i.e. F=1/t³E. Inalternate non-limiting embodiments, the flexibility of the second layercan be at least 0.5 in⁻¹ lb⁻¹; or at least 100 in⁻¹ lb⁻¹; or from 1 in⁻¹lb⁻¹ to 100 in⁻¹ lb⁻¹.

[0038] In a non-limiting embodiment, the second layer can have acompressibility which allows the polishing pad to substantially conformto the surface of the article to be polished. The surface of amicroelectronic substrate, such as a semiconductor wafer, can have a“wave” contour as a result of the manufacturing process. It iscontemplated that if the polishing pad cannot adequately conform to the“wave” contour of the substrate surface, the uniformity of the polishingperformance can be degraded. For example, if the pad substantiallyconforms the ends of the “wave”, but cannot substantially conform andcontact the middle portion of the “wave”, only the ends of the “wave”can be polished or planarized and the middle portion can remainsubstantially unpolished or unplanarized.

[0039] The compressibility of the second layer can vary. As previouslydescribed, the term “compressibility” refers to the percent volumecompressibility measurement. In alternate non-limiting embodiments, thepercent volume compressibility of the second layer can be at least onepercent; or three percent or less; or from one to three percent.

[0040] The percent volume compressibility can be determined using avariety of conventional methods known in the art. In a non-limitingembodiment, the percent volume compressibility is determined aspreviously described herein.

[0041] In another non-limiting embodiment, the second layer candistribute the compressive forces experienced by the first layer over alarger area of an optional third layer. In a non-limiting embodiment,the second layer is substantially non-volume compressible.

[0042] In another non-limiting embodiment, the second layer can functionas a substantial barrier to fluid transport between the first layer andan optional third layer at least partially connected to the secondlayer. Thus, a consideration in selecting the material comprising thesecond layer can be the ability of the material to substantially reduce,minimize or essentially prevent the transport of polishing slurry fromthe first layer to an optional third layer. In a non-limitingembodiment, the second layer can be substantially impermeable to thepolishing slurry such that the optional third layer does not becomesaturated with polishing slurry.

[0043] In an alternate non-limiting embodiment, the second layer can beperforated such that polishing slurry can penetrate the first and secondlayers to wet an optional third layer. In a further non-limitingembodiment, the optional third layer can be substantially saturated withpolishing slurry. The perforations in the second layer can be formed bya variety of techniques known to the skilled artisan, such as but notlimited to punching, die cutting, laser cutting or water jet cutting.The hole size, number and configuration of the perforations can vary. Ina non-limiting embodiment, the perforation hole diameter can be at least{fraction (1/16)} inch with at least 26 holes per square inch in astaggered hole pattern.

[0044] In a non-limiting embodiment, the first layer can be connected toat least a portion of the second layer to produce a stacked padassembly. As used herein and the claims, the term “connected to” meansto link together or place in relationship either directly, or indirectlyby one or more intervening materials. In a non-limiting embodiment, thefirst and second layers are at least partially connected such that theopening of the first layer can be at least partially aligned with the atleast partially transparent window of the second layer.

[0045] In a non-limiting embodiment, the first layer of the polishingpad can be connected to at least a portion of the second layer using anadhesive. A suitable adhesive for use in the present invention canprovide sufficient peel resistance such that the pad layers essentiallyremain in place during use. Further, the adhesive can be selected tosufficiently withstand shear stresses which are present during thepolishing or planarization process and moreover, can sufficiently resistchemical and moisture degradation during use. The adhesive can beapplied using conventional techniques known to the skilled artisan. In anon-limiting embodiment, the adhesive can be applied to a lower surfaceof the first layer and/or an upper surface of the second layer which areparallel facing to one another.

[0046] The adhesive can be chosen from a wide variety of adhesivematerials known in the art, such as but not limited to contactadhesives, pressure sensitive adhesives, structural adhesives, hot meltadhesives, thermoplastic adhesives, and curable adhesives, such asthermosetting adhesives. Non-limiting examples of structural adhesivescan be chosen from polyurethane adhesives, and epoxy resin adhesives;such as those based on the diglycidyl ether of bisphenol A. Non-limitingexamples of pressure sensitive adhesives can include an elastomericpolymer and a tackifying resin.

[0047] The elastomeric polymer can be chosen from natural rubber, butylrubber, chlorinated rubber, polyisobutylene, poly(vinyl alkyl ethers),alkyd adhesives, acrylics such as those based on copolymers of2-ethylhexyl acrylate and acrylic acid, block copolymers such asstyrene-butadiene-styrene, and mixtures thereof. In a non-limitingembodiment, a pressure sensitive adhesive can be applied to a substrateusing an organic solvent such as toluene or hexane, or from awater-based emulsion or from a melt. As used herein, “hot melt adhesive”refers to an adhesive comprised of a nonvolatile thermoplastic materialthat can be heated to a melt, then applied to a substrate as a liquid.Non-limiting examples of hot melt adhesives can be chosen fromethylene-vinyl acetate copolymers, styrene-butadiene copolymers,ethylene-ethyl acrylate copolymers, polyesters, polyamides such as thoseformed from the reaction of a diamine and a dimer acid, andpolyurethanes.

[0048] In a non-limiting embodiment of the present invention, the firstlayer can comprise an opening. In a further non-limiting embodiment, atleast a portion of the second layer can comprise a window which is atleast partially transparent to wavelengths used by the metrologyinstrumentation of the planarizing equipment. The size, shape, andpositioning of the opening in the first layer and/or the window in thesecond layer can be dependent upon the metrology instrumentation andpolishing apparatus being employed to polish and/or planarize the pad.The opening can be produced by a variety of conventional methods knownin the art. In alternate non-limiting embodiments, the opening can bemade by punching, die cutting, laser cutting or water jet cutting. In afurther non-limiting embodiment, the opening can be formed by moldingthe first layer. In an alternate non-limiting embodiment, the openingscan be die cut into the first layer using an NAEF Model B die pressfitted with dies of suitable size and shape, which are commerciallyavailable from MS Instruments Company, Stony Brook, N.Y.

[0049] In a non-limiting embodiment, the opening in the first layer canbe produced prior to stacking together and/or at least partiallyconnecting the first layer with the second layer.

[0050] At least a portion of the second layer can comprise an at leastpartially transparent window. In a non-limiting embodiment, the secondlayer can comprise an at least partially transparent material. Inanother non-limiting embodiment, the second layer can comprise asubstantially non-transparent material; an opening can be cut into thesecond layer to remove a portion of the second layer; an at leastpartially transparent material can be inserted into the opening in thesecond layer. The opening can be made using a variety of methodspreviously described herein. In a non-limiting example, the second layercan include a metal foil; an opening can be cut into the metal foil toremove a portion of the metal foil; a piece of polyester can be cut intoa size and shape that substantially corresponds to the opening; thepolyester can be fitted into the opening in the metal foil to form an atleast partially transparent window.

[0051] In a non-limiting embodiment, the second layer can comprise anadhesive assembly. The adhesive assembly can include interposing thesecond layer between an upper adhesive layer and a lower adhesive layer.In a non-limiting embodiment, the upper adhesive layer of the adhesiveassembly can be at least partially connected to the lower surface of thefirst layer. The lower adhesive layer of the adhesive assembly can be atleast partially connected to the upper surface of an optional thirdlayer. The second layer of the adhesive assembly can be selected fromthe aforementioned suitable materials for the second layer of thepolishing pad. The upper and lower adhesive layers of the adhesiveassembly can be selected from the non-limiting examples of adhesivespreviously mentioned herein. In a non-limiting embodiment, the upper andlower adhesive layers each can be contact adhesives. The adhesiveassembly can be referred to in the art as two-sided or double coatedtape. Non-limiting examples of commercially available adhesiveassemblies include those from 3M, Industrial Tape and SpecialtiesDivision.

[0052] In a further non-limiting embodiment, at least a portion of theadhesive layer can be removed from the second layer of the adhesiveassembly exposing at least a portion of the at least partiallytransparent middle layer of the adhesive assembly, thereby forming an atleast partially transparent window in the second layer. In alternatenon-limiting embodiments, the removal of the adhesive can be performedprior to stacking the layers or after the layers are stacked. Theremoval process can include a variety of methods known to the skilledartisan, including but not limited to dissolution of the adhesive insolvent or aqueous detergent solution, or physically stripping theadhesive from the second layer. In a non-limiting embodiment, physicallystripping the adhesive can be include contacting the adhesive with amaterial to which the adhesive substantially adheres, and then pullingthe material from the second layer, whereby the adhesive is removed withthe material.

[0053] In a further non-limiting embodiment, the window of the secondlayer can be recessed below the polishing surface of the pad by adistance equal to the thickness of the first layer of the pad.

[0054] In another non-limiting embodiment, the pad assembly can includea coating on at least a portion of the top and/or bottom sides of thewindow of the second layer. The coating can be at least partiallyapplied with an adhesive in place or following removal of the adhesive.The coating can be at least partially applied prior to stacking thelayers or after the layers have been stacked. The coating can provideany one of the following properties, for example: improved transparencyof the window area, improved abrasion resistance, improved punctureresistance. In a non-limiting embodiment, the coating can include aresin film, or a cast-in-place resin coating.

[0055] Non-limiting examples of suitable resin films for use in thepresent invention can include the materials described above for thesecond layer. In alternative non-limiting embodiments, the resin filmchosen for the coating can be the same material or different material asthat comprising the second pad layer. The resin film can be at leastpartially adhered to the window area of the second layer by any meansknown to the skilled artisan, such as the adhesive methods and materialslisted above for pad stack adhesives. In a non-limiting embodiment, thecoating can be a layer of resin film that can be the same as thematerial used for the second layer. The coating can be at leastpartially applied after assembly of the pad stack. The coating can be atleast partially applied to both the top and bottom surfaces of thewindow area of the second layer, and the adhesive can be at leastpartially adhered using a contact adhesive used as the stack adhesive.

[0056] In a non-limiting embodiment, the coating can be a cast-in-placeresin coating, which can be applied as a liquid, as a solvent solution,dispersion, or aqueous latex; as a melt, or as a blend of resinprecursors that can react to form the coating. The application of theliquid can be accomplished by a variety of known methods, includingspraying, padding, and pouring. Non-limiting examples of suitablematerials for the coating include thermoplastic acrylic resins,thermoset acrylic resins, such as hydroxyl-functional acrylic latexescrosslinked with urea-formaldehyde or melamine-formaldehyde resins,hydroxyl-functional acrylic resins crosslinked with epoxy resins, orcarboxyfunctional acrylic latexes crosslinked with carbodiimides orpolyimines or epoxy resins; urethane systems, such as hydroxyfunctionalacrylic resin crosslinked with polyisocyanate, moisture-curedisocyanate-terminated resins; carbamate-funtional acrylic resinscrosslinked with melamine-formaldehyde resins; epoxy resins, such aspolyamide resin crosslinked with bisphenol A epoxy resins, phenolicresins crosslinked with bisphenol A epoxy resins; polyester resins, suchas hydroxyl-terminated polyesters crosslinked with melamine-formaldehyderesins or with polyisocyanates or with epoxy crosslinkers.

[0057] In a non-limiting embodiment, the coating can be an aqueousacrylic latex, which can be applied following stacking of the padassembly. The coating can be at least partially applied to the top andbottom surfaces of the window area of the second layer. Application ofthe coating can be performed following removal of an adhesive from thewindow area.

[0058] The window pad of the present invention can be used with avariety of polishing equipment known in the art. In a non-limitingembodiment, a Mirra polisher, produced by Applied Materials Inc, SantaClara Calif., can be used wherein the shape of the opening is arectangle, having a size 0.5″×2″, being positioned with the long axisradially oriented and centered 4″ from the center of the pad. The platenfor the Mirra polisher is 20″ in diameter. A pad for use with thispolisher can comprise a circle of a 20-inch diameter having a windowlocated in the area as described.

[0059] In a further non-limiting embodiment, a Teres polishercommercially available from Lam Research Corporation, Fremont, Calif.,can be employed. This polisher uses a continuous belt instead of acircular platen. The pad for this polisher can be a continuous belt of12″ width and 93.25″ circumference, which has a window area suitablysized and positioned to align with the metrology window of the Terespolisher can be such that it can be at least partially aligned with theat least partially transparent window in the second layer.

[0060] As identified previously herein, the polishing pad of the presentinvention can comprise additional optional layer(s). The additionallayer(s) can contain opening(s) that are substantially aligned with theopening in the first layer and the at least partially transparent windowin the second layer.

[0061] In a non-limiting embodiment, the polishing pad of the presentinvention can comprise a third layer. The third layer can function asthe bottom layer of the pad which can be attached to the platen of thepolishing apparatus.

[0062] In a non-limiting embodiment, the third layer can comprise amaterial that is softer than the first layer. As used herein, the term“softness” refers to the Shore A Hardness of the material. The softerthe material, the lower the Shore A Hardness value. Thus, in the presentinvention, the Shore A Hardness value of the third layer can be lowerthan the Shore A Hardness value of the first layer. In a non-limitingembodiment, the third layer can have a Shore A Hardness of at least 15.In alternate non-limiting embodiments, the Shore A Hardness of the thirdlayer can be at least 45, or 75 or less, or from 45 to 75. The Shore AHardness can be determined using a variety of conventional methods knownin the art. In a non-limiting embodiment, the Shore A Hardness can bedetermined as previously described herein.

[0063] In a non-limiting embodiment, the third layer can be used toincrease the uniformity of contact between the polishing pad and thesurface of the substrate undergoing polishing.

[0064] In a non-limiting embodiment of the present invention, thematerial comprising the third layer of the polishing pad can have acompressibility greater than the material comprising the first layer. Aspreviously described, the term “compressibility” refers to the percentvolume compressibility measurement. Thus, the percent volumecompressibility of the third layer is greater than the percent volumecompressibility of the first layer. In a non-limiting embodiment, thepercent volume compressibility of the third layer can be less than 20percent when a load of 20 psi is applied. In alternate non-limitingembodiments, the percent volume compressibility of the third layer canbe less than 10 percent when a load of 20 psi is applied, or less than 5percent when a load of 20 psi is applied. As previously identifiedpercent volume compressibility can be determined by a variety ofconventional methods known in the art. In a non-limiting embodiment,percent volume compressibility can be determined as previously describedherein.

[0065] The thickness of the third layer can vary. In general, the thirdlayer thickness should be such that the pad is not too thick. A padwhich is too thick can be difficult to place on and take off of theplanarization equipment. Thus, in alternate non-limiting embodiments,the thickness of the first layer can be at least 0.040 inches, or atleast 0.045 inches; or 0.100 inches or less, or 0.080 inches or less, or0.065 inches or less.

[0066] The sublayer can comprise a wide variety of materials known inthe art. Suitable materials can include natural rubber, syntheticrubbers, thermoplastic elastomer, foam sheet and combinations thereof.The material of the sublayer can be foamed or blown to produce a porousstructure. The porous structure can be open cell, closed cell, orcombinations thereof. Non-limiting examples of synthetic rubbers caninclude neoprene rubber, silicone rubber, chloroprene rubber,ethylene-propylene rubber, butyl rubber, polybutadiene rubber,polyisoprene rubber, EPDM polymers, styrene-butadiene copolymers,copolymers of ethylene and ethyl vinyl acetate, neoprene/vinyl nitrilerubber, neoprene/EPDM/SBR rubber, and combinations thereof. Non-limitingexamples of thermoplastic elastomers can include polyolefins,polyesters, polyamides, polyurethanes such as those based on polyethersand polyesters, and copolymers thereof. Non-limiting examples of foamsheet can include ethylene vinyl acetate sheets and polyethylene foamsheets, such as but not limited to those which are commerciallyavailable from Sentinel Products, Hyannis, N.J.; polyurethane foamsheets, such as but not limited to those which are commerciallyavailable from Illbruck, Inc., Minneapolis, Minn.; and polyurethane foamsheets, and polyolefin foam sheets, such as but not limited to thosewhich are available from Rogers Corporation, Woodstock, Conn. In afurther non-limiting embodiment, the sublayer can include non-woven orwoven fiber mat, and combinations thereof; such as but not limited topolyolefin, polyester, polyamide, or acrylic fibers, which have beenimpregnated with a resin. The fibers can be staple or substantiallycontinuous in the fiber mat. Non-limiting examples can include but arenot limited to non-woven fabric impregnated with polyurethane asdescribe in U.S. Pat. No. 4,728,552, such as polyurethane impregnatedfelt. A non-limiting example of a commercially available non-wovensubpad can be Suba™ IV, from Rodel, Inc. Newark Del.

[0067] In the present invention, the optional third layer can comprisean opening. In alternate non-limiting embodiments, the opening can beproduced by any suitable means known in the art, such as thosepreviously identified relative to the opening in the first layer.Further, as previously identified, the size, shape and position of theopening can be dependent upon the metrology instrumentation andpolishing apparatus employed.

[0068] In a non-limiting embodiment, the third layer can be at leastpartially connected to the second layer and can be in contact with thebase of the planarizing machine. The third layer can contain an openingthat is at least partially aligned with the opening of the first layerand the at least partially transparent or window area of the secondlayer.

[0069] In an alternate non-limiting embodiment, the first layer of thepolishing pad can be connected to at least a portion of the second layerand the second layer can be connected to at least a portion of a thirdlayer using an adhesive. Suitable adhesives can include those previouslyrecited herein.

[0070] In a further non-limiting embodiment, the polishing pad of thepresent invention can comprise a first layer, a second layer, and athird layer. The first and third layers each comprise an opening. Theopening of the first and third layers can be at least partially alignedwith one another. At least a portion of the second layer can include anat least partially transparent window. The window can be at leastpartially coated on both sides with contact adhesive, and the layers canbe pressed together to form a stacked pad assembly. The adhesive canthen be physically stripped from the top and bottom surface of thewindow area of the second layer using a material to which the adhesivesubstantially adheres. A non-limiting example of a material to which theadhesive substantially adheres is Teslin® SP-100 0, a synthetic sheetmaterial which is commercially available from PPG Industries, Inc,Pittsburgh, Pa.

[0071] The polishing pads of the present invention can be used incombination with polishing slurrys, such as polishing slurries, whichare known in the art. Non-limiting examples of suitable slurries for usewith the pad of the present invention, include but are not limited tothe slurries disclosed in U.S. patent application Ser. Nos. 09/882,548and 09/882, 549, which were both filed on Jun. 14, 2001 and are pending.In a non-limiting embodiment, the polishing slurry can be interposedbetween the first layer of the pad and the substrate to be polished. Thepolishing or planarizing process can include moving the polishing padrelative to the substrate being polished. A variety of polishing slurrysor slurries are known in the art. Non-limiting examples of suitableslurries for use in the present invention include slurries comprisingabrasive particles. Abrasives that can be used in the slurries includeparticulate cerium oxide, particulate alumina, particulate silica andthe like. Examples of commercial slurries for use in the polishing ofsemiconductor substrates include but are not limited to ILD1200 andILD1300 available from Rodel, Inc. Newark Del. and Semi-Sperse AM100 andSemi-Sperse 12 available from Cabot Microelectronics Materials Division,Aurora, Ill.

[0072] In a non-limiting embodiment, the polishing pad of the presentinvention can be utilized with an apparatus for planarizing an articlehaving a non-planar surface. The planarizing apparatus can include aretaining means for holding the article; and a motive power means formoving the pad and the retaining means with respect to the other suchthat movement of the pad and the retaining means causes the slurry andthe planarizing surface of the pad to contact and planarize thenon-planar surface of the article. In a further non-limiting embodiment,the planarizing apparatus can include a means of renewing the polishingor planarizing surface of the pad. A non-limiting example of a suitablerenewing means includes a mechanical arm equipped with an abrasive diskwhich abrades the work surface of the pad.

[0073] In an alternate non-limiting embodiment, the planarizingapparatus can include an apparatus for conducting in-situ metrology ofthe article being polished or planarized. Commercial polishing orplanarizing apparatuses are available from equipment manufacturers suchas Applied Materials, LAM Research, SpeedFam-IPEC, and Ebara Corp.

[0074] In a non-limiting embodiment, the pad of the present inventioncan be placed on a cylindrical metal base; and can be connected to atleast a portion of the base with a layer of adhesive. Suitable adhesivescan include a wide variety of known adhesives. In a further non-limitingexample, the pad can be placed on the cylindrical metal base or platenof a polishing or planarizing apparatus that includes a means ofconducting in-situ metrology of the article being polished. The pad canbe placed such that its window can be aligned with the metrology windowof the platen.

EXAMPLE 1

[0075] A polishing pad with a window was prepared as follows:

[0076] 1. A first layer was prepared according to Recipe A describedbelow.

[0077] 2. A ½″×2″ rectangular hole was cut into the first layer using astraight-edge and a scalpel-style utility knife.

[0078] 3. A second layer was formed using High Performance Double CoatedTape 9500PC, commercially obtained from 3M Industrial Tape andSpecialties Division. The adhesive layer of the tape was adhered to thebottom side of the first layer such that the rectangular opening in thefirst layer was substantially spanned by the tape.

[0079] 4. A third layer was formed using a 0.060″ thick sheet ofpolyurethane foam, having trade name PORON 4701-50, commerciallyobtained from Rogers Corporation. A ½″×2″ rectangular hole was cut intothe third layer using a straight-edge and a scalpel-style utility knife.

[0080] 5. The third layer was adhered to the second layer by removingthe release paper from the second layer and applying the third layer tothe adhesive film thus exposed. The third layer was positioned such thatthe rectangular openings in the first layer and the third layer weresubstantially aligned.

[0081] 6. The three-layer stack assembly was then pressed together andpassed through a calendar roll set.

[0082] 7. A window was formed by removing a portion of the adhesive onthe upper and lower sides of the second layer. The adhesive was removedby contacting it with a ½″×2″ rectangular piece of Teslin SP-1000,commercially available from PPG Industries, Incorporated, pressing thepiece by hand to ensure good contact between the adhesive and the TeslinSP-1000, then peeling away the Teslin SP-1000. The adhesive selectivelyadhered to the Teslin SP-1000, leaving the substantially clear film ofthe window free of adhesive.

[0083] The resulting pad stack had a rectangular window having a size of½″×2″.

[0084] Recipe A for Pad First Layer:

[0085] Step 1

[0086] Particulate crosslinked polyurethane was prepared using theingredients listed in Table A. TABLE A Ingredients Weight (grams) Charge1 diamine curative (a) 810 surfactant (b) 30.6 methyl isobutyl ketonesolvent 822 Charge 2 isocyanate functional prepolymer (c) 2112

[0087] Charge 1 was added to an open container and warmed with stirringon a hot plate until the contents of the container reached a temperatureof 35° C. Stirring was continued at this temperature until theingredients formed a substantially homogeneous solution. The containerwas then removed from the hot plate. Charge 2 was warmed to atemperature of 55° C. using a water bath then added to Charge 1. Thecontents were mixed for a period of three (3) minutes with a motordriven impeller until uniform. The contents of the container were thenquickly poured into 10 kilograms of deionized water at a temperature of40° C., with concurrent vigorous stirring of the deionized water. Uponcompletion of the addition of the contents of the container, vigorousmixing of the deionized water was continued for an additional 60minutes. The wet particulate crosslinked polyurethane was classifiedusing a stack of two sieves. The top sieve had a mesh size of 50 mesh(300 micron sieve openings), and the bottom sieve had a mesh size of 140mesh (105 micron sieve openings). The isolated particulate crosslinkedpolyurethane from the 140 mesh was dried overnight in an oven at atemperature of 80° C.

[0088] Step 2:

[0089] A polishing pad comprising particulate crosslinked polyurethaneand crosslinked polyurethane binder was prepared using the ingredientssummarized in the following Table B. TABLE B Ingredients Weight (grams)Charge 1 particulate crosslinked polyurethane 918 of Step 1 Charge 2isocyanate functional prepolymer (c) 265 aliphatic polyisocyanate (d)8.5 additive (e) 8.5 acetone solvent 62

[0090] Charge 2 was mixed until substantially homogeneous, using a motordriven stainless steel impeller. The substantially homogenous mixture ofCharge 2 was then combined with Charge 1 in a suitable container andmixed together by means of a motor driven mixer. A 1040 gram portion ofthe combination of Charges 1 and 2 was then introduced onto a 26″×26″flat mold. The mold was fed through a pair of rollers at ambienttemperature to form a sheet that was 0.100″ thick. The sheet was curedat a temperature of 25° C. and 80% relative humidity for 18 hours,followed by a temperature of 130° C. for 1 hour. Circular pads with a22.5″ diameter were cut from the sheet then the upper and lower surfacesof the pad were made parallel using a milling machine.

[0091] The resulting pad was used as the first layer in Example 1.

In the claims:
 1. A polishing pad comprising: a. a first layer having anopening; and b. a second layer wherein at least a portion of said secondlayer comprises an at least partially transparent window, and whereinsaid first layer is at least partially connected to said second layer,and wherein said first layer absorbs at least two percent by weight ofpolishing slurry based on total weight of said first layer.
 2. Thepolishing pad of claim 1 wherein said first layer absorbs 50% or less byweight of polishing slurry based on total weight of said first layer. 3.The polishing pad of claim 1 wherein said first layer is selected fromparticulate polymer and crosslinked polymer binder; particulate polymerand an organic polymer binder; sintered particles of thermoplasticresin; pressure sintered powder compacts of thermoplastic polymer;polymeric matrices impregnated with a plurality of polymericmicroelements wherein each polymeric microelement can have a void spacetherein, or combinations thereof.
 4. The polishing pad of claim 1wherein said first layer has a thickness of at least 0.020 inches. 5.The polishing pad of claim 4 wherein said first layer has a thickness of0.150 inches or less.
 6. The polishing pad of claim 1 wherein saidsecond layer is selected from substantially non-volume compressiblepolymers and metallic films and foils.
 7. The polishing pad of claim 1wherein said second layer is selected from polyolefins; cellulose-basedpolymers; acrylics; polyesters and co-polyesters; polycarbonate;polyamides; high performance plastics; or mixtures thereof.
 8. Thepolishing pad of claim 1 wherein said second layer is selected from lowdensity polyethylene, high density polyethylene ultra-high molecularweight polyethylene or polypropylene; cellulose acetate or cellulosebutyrate; PET or PETG; nylon 6/6 or nylon 6/12; polyetheretherketone,polyphenylene oxide, polysulfone, polyimide, or polyetherimide; ormixtures thereof.
 9. The polishing pad of claim 1 wherein said secondlayer has a thickness of at least 0.0005 inches.
 10. The polishing padof claim 9 wherein said second layer has a thickness of 0.0650 inches orless.
 11. The polishing pad of claim 1 wherein said first and secondlayers are at least partially connected by an adhesive material.
 12. Thepolishing pad of claim 11 wherein said adhesive material is selectedfrom contact adhesives, pressure sensitive adhesives, structuraladhesives, hot melt adhesives, thermoplastic adhesives, and curableadhesives, thermosetting adhesives; and combinations thereof.
 13. Thepolishing pad of claim 1 wherein said opening in said first layer is atleast partially aligned with said window in said second layer.
 14. Thepolishing pad of claim 1 further comprising a third layer at leastpartially connected to said second layer, said third layer having anopening.
 15. The polishing pad of claim 14 wherein said third layer isselected from natural rubber, synthetic rubbers, thermoplasticelastomer, foam sheet and combinations thereof.
 16. The polishing pad ofclaim 14 wherein said third layer has a thickness of at least 0.04inches.
 17. The polishing pad of claim 16 wherein said third layer has athickness of 0.100 inches or less.
 18. The polishing pad of claim 14wherein said first, second and third layers are at least partiallyconnected by an adhesive material.
 19. The polishing pad of claim 14wherein said opening in said first layer, said window in said secondlayer and said opening in said third layer are at least partiallyaligned.
 20. A polishing pad comprising: a. a first layer having anopening; and b. a second layer wherein at least a portion of said secondlayer comprises an at least partially transparent window, and whereinsaid first layer is at least partially connected to said second layer,and wherein said first layer has a porosity of at least two percent byvolume based on total volume of said first layer.
 21. The polishing padof claim 20 wherein said first layer has a porosity of 50% or less byvolume based on total volume of said first layer.
 22. The polishing padof claim 20 wherein said first layer is selected from particulatepolymer and crosslinked polymer binder; particulate polymer and anorganic polymer binder; sintered particles of thermoplastic resin;pressure sintered powder compacts of thermoplastic polymer; polymericmatrices impregnated with a plurality of polymeric microelements whereineach polymeric microelement can have a void space therein, orcombinations thereof.
 23. The polishing pad of claim 20 wherein saidfirst layer has a thickness of at least 0.020 inches.
 24. The polishingpad of claim 23 wherein said first layer has a thickness of 0.150 inchesor less.
 25. The polishing pad of claim 20 wherein said second layer isselected from substantially non-volume compressible polymers andmetallic films and foils.
 26. The polishing pad of claim 20 wherein saidsecond layer is selected from polyolefins; cellulose-based polymers;acrylics; polyesters and co-polyesters; polycarbonate; polyamides; highperformance plastics; or mixtures thereof.
 27. The polishing pad ofclaim 1 wherein said second layer is selected from low densitypolyethylene, high density polyethylene ultra-high molecular weightpolyethylene or polypropylene; cellulose acetate or cellulose butyrate;PET or PETG; nylon 6/6 or nylon 6/12; polyetheretherketone,polyphenylene oxide, polysulfone, polyimide, or polyetherimide; ormixtures thereof.
 28. The polishing pad of claim 20 wherein said secondlayer has a thickness of at least 0.0005 inches.
 29. The polishing padof claim 28 wherein said second layer has a thickness of 0.0650 inchesor less.
 30. The polishing pad of claim 20 wherein said first and secondlayers are at least partially connected by an adhesive material.
 31. Thepolishing pad of claim 30 wherein said adhesive material is selectedfrom contact adhesives, pressure sensitive adhesives, structuraladhesives, hot melt adhesives, thermoplastic adhesives, curableadhesives, thermosetting adhesives and combinations thereof.
 32. Thepolishing pad of claim 20 wherein said opening in said first layer is atleast partially aligned with said window in said second layer.
 33. Thepolishing pad of claim 20 further comprising a third layer at leastpartially connected to said second layer, said third layer having anopening.
 34. The polishing pad of claim 33 wherein said third layer isselected from natural rubber, synthetic rubbers, thermoplasticelastomer, foam sheet and combinations thereof.
 35. The polishing pad ofclaim 33 wherein said third layer has a thickness of at least 0.04inches.
 36. The polishing pad of claim 35 wherein said third layer has athickness of 0.100 inches or less.
 37. The polishing pad of claim 30wherein said first, second and third layers are at least partiallyconnected by an adhesive material.
 38. The polishing pad of claim 30wherein said opening in said first layer, said window in said secondlayer and said opening in said third layer are at least partiallyaligned.
 39. A polishing pad comprising: a. a first layer having anopening; and b. a second layer wherein at least a portion of said secondlayer comprises an at least partially transparent window, and whereinsaid first layer is at least partially connected to said second layer,and wherein said first layer has a percent volume compressibilitygreater than said second layer.
 40. The polishing pad of claim 39wherein said first layer has a percent volume compressibility of atleast 0.3% when a load of 20 psi is applied.
 41. The polishing pad ofclaim 40 wherein said first layer has a percent volume compressibilityof 3% or less when a load of 20 psi is applied.
 42. The polishing pad ofclaim 39 wherein said second layer is substantially non-volumecompressible.
 43. The polishing pad of claim 39 wherein said first layeris selected from particulate polymer and crosslinked polymer binder;particulate polymer and an organic polymer binder; sintered particles ofthermoplastic resin; pressure sintered powder compacts of thermoplasticpolymer; polymeric matrices impregnated with a plurality of polymericmicroelements wherein each polymeric microelement can have a void spacetherein, or combinations thereof.
 44. The polishing pad of claim 39wherein said second layer is selected from substantially non-volumecompressible polymers and metallic films and foils.
 45. The polishingpad of claim 39 wherein said second layer is selected from polyolefins;cellulose-based polymers; acrylics; polyesters and co-polyesters;polycarbonate; polyamides; high performance plastics; or mixturesthereof.
 46. The polishing pad of claim 39 wherein said second layer isselected from low density polyethylene, high density polyethyleneultra-high molecular weight polyethylene or polypropylene; celluloseacetate or cellulose butyrate; PET or PETG; nylon 6/6 or nylon 6/12;polyetheretherketone, polyphenylene oxide, polysulfone, polyimide, orpolyetherimide; or mixtures thereof.
 47. The polishing pad of claim 39wherein said first and second layers are at least partially connected byan adhesive material.
 48. The polishing pad of claim 47 wherein saidadhesive material is selected from contact adhesives, pressure sensitiveadhesives, structural adhesives, hot melt adhesives, thermoplasticadhesives, curable adhesives, thermosetting adhesives and combinationsthereof.
 49. The polishing pad of claim 39 wherein said opening in saidfirst layer is at least partially aligned with said window in saidsecond layer.
 50. The polishing pad of claim 39 further comprising athird layer at least partially connected to said second layer, saidthird layer having an opening.
 51. The polishing pad of claim 50 whereinsaid third layer is selected from natural rubber, synthetic rubbers,thermoplastic elastomer, foam sheet and combinations thereof.
 52. Thepolishing pad of claim 50 wherein said first, second and third layersare at least partially connected by an adhesive material.
 53. Thepolishing pad of claim 50 wherein said opening in said first layer, saidwindow in said second layer and said opening in said third layer are atleast partially aligned.
 54. The polishing pad of claim 39 wherein atleast a portion of said window comprises a coating.
 55. The polishingpad of claim 54 wherein said coating comprises a resin coating.
 56. Thepolishing pad of claim 55 wherein said resin coating is selected fromthermoplastic acrylic resins, thermoset acrylic resins, urethanesystems, epoxy resins, polyester resins, or mixtures thereof.
 57. Thepolishing pad of claim 39 wherein said first layer comprises grooves ona polishing surface.
 58. The polishing pad of claim 39 wherein saidfirst layer comprises a pattern on a polishing surface.
 59. A method ofpreparing a polishing pad comprising at least partially connecting afirst layer having an opening to a second layer, wherein at least aportion of said second layer comprises an at least partially transparentwindow, and wherein said first layer absorbs at least two percent byweight of polishing slurry based on total weight of said first layer.60. The method of claim 59 further comprising at least partiallyconnecting a third layer having an opening to said second layer.
 61. Themethod of claim 59 wherein said first and second layers are at leastpartially connected by an adhesive material.
 62. A method of preparing apolishing pad comprising at least partially connecting a first layerhaving an opening to a second layer, wherein at least a portion of saidsecond layer comprises an at least partially transparent window, andwherein said first layer has a porosity of at least two percent byvolume based on total volume of said first layer.
 63. The method ofclaim 62 further comprising at least partially connecting a third layerhaving an opening to said second layer.
 64. The method of claim 62wherein said first and second layers are at least partially connected byan adhesive material.
 65. A method of preparing a polishing padcomprising at least partially connecting a first layer having an openingto a second layer, wherein at least a portion of said second layercomprises an at least partially transparent window, and wherein firstlayer has a percent volume compressibility greater than said secondlayer.
 66. The method of claim 65 further comprising at least partiallyconnecting a third layer having an opening to said second layer.
 67. Themethod of claim 65 wherein said first and second layers are at leastpartially connected by an adhesive material.
 68. A polishing padcomprising: a. a first layer having an opening; b. a second layerwherein at least a portion of said second layer comprises an at leastpartially transparent window; and c. a third layer having an opening,wherein said first layer is at least partially connected to said secondlayer and said second layer is at least partially connected to saidthird layer, and wherein said third layer is softer than said firstlayer.